Integrated circuits are used in many different applications, some of which expose the integrated circuits to extreme ambient temperatures. In some devices, particularly those that utilize relatively high power, the high ambient temperature in combination with high internal power dissipation can cause the device's internal temperature to rise to extreme levels, potentially causing damage or failure.
An over-temperature detector is configured to detect those potentially damaging high-temperature conditions and provide an output signal that may be utilized by an external system to take an appropriate mitigating action. In some cases, this may involve shutting down or reducing power dissipated in the integrated circuit.
One approach for detecting temperature in such a detector involves monitoring variations in the base-emitter voltages (VBE) of combinations of bipolar transistors, where VBE is temperature- and bias current-dependent. When a particular temperature threshold is reached or exceeded, an output of the over-temperature detector changes state (e.g., from a low value to a high value) indicating that an over-temperature condition has been detected.
Because the accuracy of such an over-temperature detector is dependent upon the electrical characteristics of the transistors, which themselves are derived from the physical geometry and doping of the transistors, any variances or defects in manufacturing process can affect the accuracy of the detector. As such it can be important to test the accuracy of an over-temperature detector following manufacture to confirm proper operation. But such testing can be difficult.
The majority of devices that are utilized for testing the operation of integrated circuits are unable to generate the high temperatures necessary to trigger over-temperature detection. To compensate, some over-temperature detectors may be placed in a ‘test mode’ that causes the over-temperature detector to identify an over-temperature condition at a greatly reduced ambient temperature. In essence, the test mode artificially reduces the temperature threshold for the detector by a number of degrees (e.g., 100 degrees Celsius). Although this approach enables a testing device to confirm that an over-temperature detector will, in fact, trigger an over-temperature warning signal, the test mode does not allow for an evaluation of the accuracy of the detector. Additionally, should the detector, once testing is complete, be inadvertently left in test mode, the detector may report false over-temperature conditions at the reduced temperature.